1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a method and apparatus driving a liquid crystal display capable of enhancing display quality and reducing power consumption.
2. Discussion of the Related Art
Generally, liquid crystal displays LCDs include a liquid crystal display panel having a plurality of liquid crystal cells arranged in a matrix pattern and driving circuit for driving the liquid crystal display panel. To display images, liquid crystal displays control light transmittance characteristics of each liquid crystal cell in accordance with an inputted video signal. Active matrix LCDs include a plurality of thin film transistors (TFTs) arranged within each liquid crystal cell and are capable of displaying moving images having a higher quality than passive matrix LCDs.
Referring to FIG. 1, active matrix LCDs generally include a liquid crystal display panel 2, a data driver 6 for applying a data signal to data lines DL1 to DLm arranged on the liquid crystal display panel, and a gate driver 4 for applying a scanning pulse to gate lines DL1 to DLn also arranged on the liquid crystal display panel 2.
The liquid crystal display panel 2 may include an upper glass substrate separated from a lower glass substrate by a layer of liquid crystal material. The liquid crystal display panel 2 includes m×n liquid crystal cells arranged in a matrix pattern. M data lines DL1 to DLm are arranged to cross n gate lines GL1 to GLn. TFTs are arranged where the data lines cross the gate lines and drive each liquid crystal cell (Clc). The TFTs respond to a scanning pulse by supplying a data signal, applied to the data lines DL1 to DLm, to the liquid crystal cell Clc. Gate electrodes of TFTs within a single horizontal line are connected to one of the gate lines GL1 to GLm. Source electrodes of TFTs within a single vertical line are connected to adjacent ones of the data lines DL1 to DLm. Drain electrodes of TFTs are connected adjacent ones of pixel electrodes of the liquid crystal cells Clc.
A gate driver 4 is controlled by a timing controller (not shown), generates a scanning pulse, and sequentially applies the scanning pulse to the gate lines GL1 to GLn. The gate driver 4 includes a shift register for sequentially generating a scanning pulse and a level shifter for shifting a voltage swing width of the scanning pulse such that it is suitable for driving the liquid crystal cell Clc. In response to the scanning pulse from the gate driver 4, the TFT is turned on. Accordingly, when turned on, the TFT supplies video data, applied to the data lines DL1 to DLn, to the corresponding pixel electrode within the liquid crystal cell Clc.
A data driver 6 samples and latches video data inputted from the timing controller (not shown), converts the latched video data into a pixel data voltage having a predetermined gamma compensating voltage, and applies the pixel data voltage to the data lines DL1 to DLm. The converted latched video data is synchronized with each generated scanning pulse and is applied to the data lines DL1 to DLm for each horizontal line during one horizontal period.
Liquid crystal cells within liquid crystal display panels 2 such as those illustrated in FIG. 1 may be driven using an inversion system. An inversion system inverts a polarity of the voltage of the data signals applied to the data lines both temporally and spatially. Accordingly, the rate at which liquid crystal material deteriorates may be reduced and the picture quality of the liquid crystal display may be improved.
Depending upon the nature in which the voltage of the data signals is inverted, the inversion systems used in LCDs are defined as frame inversion, line inversion, a column inversion, and dot inversion systems.
Referring to FIGS. 2A and 2B, when driven according to the frame inversion system, the polarity of the voltage of the video signals supplied to the liquid crystal cells is inverted every frame. For example, the voltage of the data signals applied to the liquid crystal cells is positive during an odd frame, as shown in FIG. 2A while the voltage of the data signals applied to the liquid crystal cells is negative during an even frame, as shown in FIG. 2B. Driving liquid crystal cells by the frame inversion system, however, is disadvantageous in that a flicker phenomenon is induced due to variations in voltage charged within the liquid crystal cells between frames is large.
Referring to FIGS. 3A and 3B, when driven according to the line inversion system, the polarity of the polarity of the voltage of the video signals supplied to liquid crystal cells connected to a gate line is opposite the polarity of the voltage of the video signals supplied to liquid crystal cells connected to adjacent gate lines. Further, the polarities of the voltages of the video signals applied to the liquid crystal cells are inverted every frame. For example, during odd frames as shown in FIG. 3A, the voltage of the data signals applied to odd numbered gate lines is positive while voltage of the data signals applied to even numbered gate lines is negative. During even frames as shown in FIG. 3B, the voltage of the data signals applied to odd numbered gate lines is negative while voltage of the data signals applied to even numbered gate lines is positive. Driving liquid crystal cells by the line inversion system, however, is disadvantageous in that a flicker phenomenon is induced in horizontal lines due to electrical cross-talk between liquid crystal cells arranged along the gate lines.
Referring to FIGS. 4A and 4B, when driven according to the column inversion system, the polarity of the voltage of the video signals supplied to liquid crystal cells connected to a data line is opposite the polarity of the voltage of the video signals supplied to the liquid crystal cells connected to adjacent data lines. Further, the polarities of the video signals applied to the liquid crystal cells are inverted every frame. For example, during odd frames as shown in FIG. 4A, the voltage of the data signals applied to odd data lines is positive while voltage of the data signals applied to even numbered data lines is negative. During even frames as shown in FIG. 4B, the voltage of the data signals applied to odd numbered data lines is negative while the voltage of the data signals applied to the even numbered data lines is positive. Driving liquid crystal cells by the column inversion system, however, is disadvantageous in that a flicker phenomenon is induced in vertical lines due to electrical cross-talk between liquid crystal cells arranged along the data lines.
Referring to FIGS. 5A and 5B, when driven according to the dot inversion system, the polarity of the voltage of the video signals supplied to a liquid crystal cells is opposite the polarity of the voltage of the video signals supplied to adjacent liquid crystal cells (e.g., liquid crystal cells connected to adjacent gate and data lines). Further, the polarities of the video signals applied to the liquid crystal cells are inverted every frame. For example, during odd frames as shown in FIG. 5A, the voltage of the data signals applied to liquid crystal cells arranged at crossings of odd numbered gate and data lines and liquid crystal cells arranged at crossings of even numbered gate and data lines is positive while the voltage of the data signals applied to liquid crystal cells arranged at crossings of odd numbered data lines and even numbered gate lines and liquid crystal cells arranged at crossings of even numbered data lines and odd numbered gate is negative. During even frames as shown in FIG. 5B, the voltage of the data signals applied to liquid crystal cells arranged at crossings of odd numbered gate and data lines and liquid crystal cells arranged at crossings of even numbered gate and data lines is negative while the voltage of the data signals applied to liquid crystal cells arranged at crossings of odd numbered data lines and even numbered gate lines and liquid crystal cells arranged at crossings of even numbered data lines and odd numbered gate is positive. Driving liquid crystal cells by the dot inversion system offsets any flicker phenomenon that may be induced between vertically or horizontally adjacent liquid crystal cells. Accordingly, pictures generated by the liquid crystal display panel driven using the dot inversion method have superior qualities over pictures generated by liquid crystal display panels driven using other inversion methods.
Use of the dot inversion system, however, is disadvantageous in that the polarity of voltage of the video signals supplied from the data driver to the data lines is inverted in horizontal and vertical directions and individual pixel voltages required by the dot inversion method are typically greater than those required by other inversion methods. Accordingly, liquid crystal displays driven using a dot inversion method typically consume a relatively large amount of power during their operation.